Posttraumatic stress disorder (PTSD) and substance use disorders (SUDs) co-occur with high frequency (Brady et al., 2004; Cottler et al., 1992; Jacobson et al., 2001), and this diagnostic co-occurrence has great clinical and public health significance. In particular, research indicates that the presence of co-occurring PTSD among individuals with a SUD is associated with heightened risk for a variety of risky and impulsive behaviors and associated negative clinical outcomes, including more severe substance use patterns (Back et al., 2000; Cottler et al., 1992; Najavits et al., 2007; Salgado et al., 2007), greater legal problems (Najavits et al., 1999, 2007; Ouimette et al., 1999), greater risky sexual and drug use behavior (Plotzker et al., 2007), greater risk for HIV infection (Hoff et al., 1997), and quicker relapse to substance use following discharge from SUD treatment (Hien et al., 2000; Ouimette et al., 1999, 2007). Further, findings that the worse treatment outcomes observed among SUD patients with (vs. without) PTSD are not the result of simply greater comorbidity in general (Ouimette et al., 1999) or a history of traumatic exposure (Hien et al., 2000) suggest that there is something unique to the presence of PTSD among substance users that places them at greater risk for negative clinical outcomes. Despite these findings, as well as preliminary findings of higher levels of risk-taking (as assessed through a laboratory-based task) in general among cocaine dependent inpatients with PTSD (vs. those without PTSD; Tull, Trotman, et al., 2009), no studies have examined the factors or contexts that precipitate risky behavior within a PTSD-SUD population, or the extent to which substance of choice influences risky behavior among PTSD-SUD patients. Thus, the proposed experimental study seeks to extend extant research in this area by examining the effect of imaginal trauma cue exposure on risk-taking among 210 trauma-exposed SUD patients (dependent on cocaine only, alcohol only, or cocaine and alcohol) with or without PTSD. On separate days, SUD patients with a history of Criterion A traumatic exposure will be exposed to a neutral cue or a personalized imaginal trauma cue. Following cue exposure, participants will complete two established behavioral measures of risk-taking, the Balloon Analogue Risk Task (Lejuez et al., 2002) and the Iowa Gambling Task (Bechara et al., 1994). We will examine the effect of trauma cue exposure (vs. neutral cue exposure), substance of choice (cocaine vs. alcohol vs. cocaine-alcohol dependence), and PTSD status (current PTSD vs. no history of PTSD) on risk-taking. We expect to find main effects of cocaine dependence and PTSD on risk-taking, as well as a three-way interaction between cue exposure, substance of choice, and PTSD status. Specifically, we expect that cocaine dependent patients with PTSD will exhibit the highest levels of risk-taking following trauma cue exposure than all other groups. Biological (salivary cortisol), physiological (heart rate, electrodermal response), and self-reported reactivity to cues will also be examined to better understand the factors that may lead to risk-taking among PTSD-SUD patients, thus speaking to its function.